Receiver device, transmitter device, reception method, and transmission method

ABSTRACT

Provided is a receiver device that can switch between transmission methods, while minimizing increase in the number of blind decryption iterations and the amount of signaling needed for acknowledgement. In this device, a receiver part ( 201 ) receives a signal mapped to any of a plurality of mapping candidates; and according to application levels established for each of the plurality of mapping candidates, a control signal processor ( 205 ) performs blind decryption of the plurality of mapping candidates, employing either a first transmission method using a single antenna port to carry out precoding based on feedback information from the receiver device, or a second transmission method involving transmission diversity employing multiple antenna ports.

BACKGROUND Technical Field

The present invention relates to a reception apparatus, a transmissionapparatus, a reception method and a transmission method.

Description of the Related Art

In recent years, accompanying the adoption of multimedia information incellular mobile communication systems, it has become common to transmitnot only speech data but also a large amount of data such as still imagedata and moving image data. Furthermore, studies have been activelyconducted in LTE-Advanced (Long Term Evolution Advanced) to realize hightransmission rates by utilizing broad radio bands, Multiple-InputMultiple-Output (MIMO) transmission technology, and interference controltechnology.

In addition, taking into consideration the introduction of variousdevices as radio communication terminals in M2M (machine to machine)communication and the like as well as an increase in the number ofmultiplexing target terminals due to MIMO transmission technology, thereis a concern regarding a shortage of resources in a mapping region forPDCCH (Physical Downlink Control Channel) that is used for a controlsignal (that is, a “PDCCH region”). If a control signal (PDCCH) cannotbe mapped due to such a resource shortage, data cannot be assigned tothe terminals. Therefore, even if a resource region in which data is tobe mapped is available, the resource region may not be used, whichcauses a decrease in the system throughput.

As a method for solving such a resource shortage, a study is beingcarried out on assigning, also in a data region (that is, “PDSCH(Physical Downlink Shared CHannel” region), control signals for radiocommunication terminal apparatuses (hereunder, abbreviated as“terminals,” UE (User Equipment)) served by a radio communication basestation apparatus (hereunder, abbreviated as “base station”). A resourceregion in which control signals for terminals served by the base stationare mapped is referred to as an Enhanced PDCCH (ePDCCH) region, aNew-PDCCH (N-PDCCH) region, an X-PDCCH region or the like. Mapping thecontrol signal (i.e., ePDCCH) in a data region as described aboveenables transmission power control on control signals transmitted to aterminal near a cell edge or interference control for interference by acontrol signal to another cell or interference from another cell to thecell provided by the base station.

Further, according to the LTE-Advanced system, in order to expand thecoverage area of each base station, relay technology has been studied inwhich a radio communication relay station apparatus (hereunder,abbreviated as “relay station”) is installed between a base station andterminals, and communication between the base station and terminals isperformed via the relay station. The use of relay technology allows aterminal that cannot communicate with the base station directly tocommunicate with the base station via the relay station. According tothe relay technology that has been introduced in the LTE-Advancedsystem, control signals for relay are assigned in a data region. Sinceit is expected that the control signals for relay may be extended foruse as control signals for terminals, a resource region in which controlsignals for relay are mapped is also referred to as an “R-PDCCH.”

In the LTE (Long Term Evolution) system, a DL grant (also referred to as“DL assignment”), which indicates a downlink (DL) data assignment, and aUL grant, which indicates an uplink (UL) data assignment are transmittedthrough a PDCCH.

In LTE-Advanced, a DL grant and a UL grant are mapped to R-PDCCH as wellas PDCCH. In the R-PDCCH, the DL grant is mapped in the first slot andthe UL grant is mapped in the second slot (refer to NPL 1). Thus, eachrelay station monitors (blind-decodes) control signals transmitted usingan R-PDCCH from a base station within a resource region indicated byhigher layer signaling from the base station (i.e., a “search space”)and thereby finds the control signal intended for the correspondingrelay station.

In this case, the base station indicates the search space correspondingto the R-PDCCH to the relay station by higher layer signaling asdescribed above.

In the LTE and LTE-Advanced systems, one RB (resource block) has 12subcarriers in the frequency domain and has a width of 0.5 msec in thetime domain. A unit in which two RBs are combined in the time domain isreferred to as an RB pair (for example, see FIG. 1). That is, an RB pairhas 12 subcarriers in the frequency domain, and has a width of 1 msec inthe time domain. When an RB pair represents a group of 12 subcarriers onthe frequency axis, the RB pair may be referred to as simply “RB.” Inaddition, in a physical layer, an RB pair is also referred to as a PRBpair (physical RB pair). A resource element (RE) is a unit defined by asingle subcarrier and a single OFDM symbol (see FIG. 1).

PDCCH and R-PDCCH have four aggregation levels, i.e., levels 1, 2, 4,and 8 (for example, see NPL 1). Levels 1, 2, 4, and 8 have, for example,six, six, two, and two “mapping candidates,” respectively. As usedherein, the term “mapping candidate” refers to a candidate region inwhich a control signal is to be mapped, and a search space is formed bya plurality of mapping candidates. When a single aggregation level isconfigured for a single terminal, a control signal is actually mapped inone of the plurality of mapping candidates of the aggregation level.FIG. 2 illustrates an example of search spaces corresponding to anR-PDCCH. The ovals represent search spaces for the aggregation levels.The multiple mapping candidates in each search space for eachaggregation level are located in a consecutive manner on VRBs (virtualresource blocks). The resource region candidates in the VRBs are mappedto PRBs (physical resource blocks) through higher layer signaling.

Studies are being conducted with respect to individually configuringsearch spaces corresponding to the ePDCCHs for terminals. Further, withrespect to the design of the ePDCCHs, part of the design of the R-PDCCHdescribed above can be used, and a design that is completely differentfrom the R-PDCCH design can also be adopted. In fact, studies are alsobeing conducted with regard to making the design of the ePDCCHs and thedesign of R-PDCCHs different from each other. In the followingdescription, mapping candidates in a search space corresponding toePDCCH may be called “ePDCCH candidates.”

As described above, a DL grant is mapped to the first slot and a ULgrant is mapped to the second slot in an R-PDCCH region. That is, aresource to which the DL grant is mapped and a resource to which the ULgrant is mapped are divided on the time axis. In contrast, for theePDCCHs, studies are being conducted with regard to dividing resourcesto which DL grants are mapped and UL grants are mapped on the frequencyaxis (that is, subcarriers or PRB pairs), and with regard to dividingREs within an RB pair into a plurality of groups.

In addition, “localized allocation” which allocates ePDCCHs collectivelyat positions close to each other on the frequency band, and “distributedallocation” which allocates the ePDCCHs by distributing ePDCCHs on thefrequency band have been studied as allocation methods for ePDCCHs (forexample, see FIG. 3). The localized allocation is an allocation methodfor obtaining a frequency scheduling gain, and can be used to allocatean ePDCCH to a resource that has favorable channel quality based onchannel quality information. The distributed allocation distributesePDCCHs on the frequency axis, and can obtain a frequency diversitygain. In the LTE-Advanced system, both a search space for localizedallocation and a search space for distributed allocation may beconfigured (for example, see FIG. 3).

LTE-Advanced defines transmission methods such as transmission throughsingle antenna port precoding and transmission through precoding usingmultiple antenna ports (e.g., see NPLs 2 and 3)

In the following description, transmission through single antenna portprecoding may be called “single antenna port transmission (“One Txport”)” and transmission through precoding using multiple antenna portsmay be called “transmission diversity using multiple antenna ports(“Multi ports Tx diversity” or simply “Tx diversity”).” In the followingdescription, the term “precoding” refers to assigning a weight to atransmission signal (multiplying a transmission signal by a weight) perantenna port or antenna. In addition, the term “layer” refers to s eachof spatially multiplexed signals and may also be called “stream.”Moreover, the term “rank” represents the number of layers. Furthermore,the term “transmission diversity” generically refers to transmission ofdata using a plurality of channels or a plurality of resources. Byapplying transmission diversity, signals are transmitted throughchannels (resources) including good channels (resources) and poorchannels (resources), and it is thereby possible to obtain averagereceiving quality. That is, the transmission diversity makes receivingquality stable without causing it to degrade considerably. For example,channels or resources used in transmission diversity are frequency,time, space, antenna ports and beams.

[Single Antenna Port Transmission]

In single antenna port transmission, a base station selects precodingbased on feedback information indicating channel quality measured by aterminal (also referred to as “closed-loop precoding” or “feedback-basedprecoding”). For this reason, single antenna port transmission is atransmission method which is effective when feedback information highlyreliable, for example, when the moving speed of a terminal is relativelylow. However, when feedback information cannot be obtained or when theterminal move relatively fast so that the feedback information is notvery reliable, the base station may select optional precoding (open-loopprocessing).

For example, single antenna port transmission is applicable to antennaport 1 (CRS (Cell specific Reference Signal)), antenna port 4 (MBMS(Multimedia Broadcast Multicast Service)), antenna port 5 (UE specificRS), antenna port 7 (DMRS (Demodulation Reference Signal)) and antennaport 8 (DMRS).

[Transmission Diversity Using Multiple Antenna Ports]

Transmission diversity using multiple antenna ports can obtain adiversity gain without requiring feedback information. For this reason,transmission diversity using multiple antenna ports is a transmissionmethod which is effective when the terminal moves relatively fast sothat the channel quality varies drastically, or when channel quality ispoor so that a diversity gain is necessary.

An example of transmission diversity using multiple antenna ports usedat rank 2 or higher is large delay CDD (Cyclic Delay Diversity) (spatialmultiplex+transmission diversity). On the other hand, transmissiondiversity using multiple antenna ports used at rank 1 is, for example,spatial frequency block coding for 2 antenna ports (SFBC: SpaceFrequency Block Code) and SFBC-FSTD (Frequency Switched TransmitDiversity) for 4 antenna ports.

For example, transmission diversity using multiple antenna ports isapplied to antenna ports 1 and 2 (CRS) and antenna ports 1, 2, 3 and 4(CRS). Note that transmission diversity using multiple antenna ports issupported in CRS, but not supported in DMRS.

CITATION LIST Non-Patent Literature

NPL 1

-   -   3GPP TS 36.216 V10.1.0 “Physical layer for relaying operation”

NPL 2

-   -   3GPP TS 36.211 V10.4.0 “Physical Channels and Modulation”

NPL 3

-   -   3GPP TS 36.212 V10.4.0 “Multiplexing and channel coding”

NPL 4

-   -   InterDigital Communications, 3GPP RAN WG1 Meeting #68,        R1-120138, “Reference Signals for ePDCCH,” February 2012

BRIEF SUMMARY Technical Problem

The number of CRS antenna ports used for demodulation of PDCCH isdetermined for each cell and is common to terminals within the samecell. The transmission method varies depending on the number of CRSantenna ports. More specifically, when the number of antenna ports is 1,precoding with the number of antenna ports of 1 (that is, single antennaport transmission) is applied, and when the number of antenna ports is 2or 4, transmission diversity for 2 antenna ports or 4 antenna ports(that is, transmission diversity using multiple antenna ports) isapplied.

When demodulating R-PDCCH, the base station indicates, to each terminal,which CRS or DMRS is to be used by higher layer signaling, and canthereby change a reference signal used for demodulation of R-PDCCH foreach terminal. However, reference signals used for demodulation ofR-PDCCH cannot be dynamically changed in subframe units. Therefore, inR-PDCCH, it is not possible to dynamically switch between transmissiondiversity using CRS and single antenna port transmission using DMRS.

In ePDCCH, studies are also being conducted on supporting both singleantenna port transmission and transmission diversity using multipleantenna ports. Moreover, in ePDCCH, studies are being conducted onsupporting transmission diversity using multiple antenna ports usingDMRS without using CRS. Therefore, in ePDCCH, when switching betweensingle antenna port transmission and transmission diversity usingmultiple antenna ports using DMRS, indication is necessary to indicateswitching between transmission methods.

However, if the ePDCCH transmission method is switched by higher layersignaling, a control delay increases and it takes time to switch betweenthe transmission methods. On the other hand, ePDCCH requires dynamicallyswitching between transmission methods in, for example, CoMP(coordinated multiple point transmission and reception) operationcontrol or interference control.

In response to the above-described demand, a method of increasing thenumber of times ePDCCH candidates are detected (number of times blinddecoding is performed) and a method of increasing control signalsindicating a transmission method are considered as the method for aterminal to select an appropriate ePDCCH transmission method.

The method of increasing the number of times ePDCCH candidates aredetected is a method of performing blind decoding by assuming aplurality of transmission methods for the same ePDCCH candidate.However, when the number of times blind decoding is performed increases,an ePDCCH reception delay may occur and this delay may also affectreception processing on data that follows.

On the other hand, the method of increasing control signals indicating atransmission method is a method of indicating a transmission method foreach ePDCCH candidate. For example, when the transmission method isswitched between transmission diversity using 2 antenna ports and singleantenna port transmission, one bit per ePDCCH candidate is necessary toindicate the transmission method. When a transmission method isindicated to each of all ePDCCH candidates (e.g., N ePDCCH candidates),N times the number of bits (e.g., 32 bits when N=32) are necessary.

In addition to the transmission method, by adding indication of variousparameters necessary for blind decoding, optimum parameters can beconfigured for each of ePDCCH candidates. Examples of theabove-described parameters are “DCI format” that determines atransmission mode, “aggregation level” that determines the number of REsforming each ePDCCH candidate, “antenna port number,” ePDCCH arrangementmethod (localized or distributed) or the like in addition to theaforementioned transmission method as shown in FIG. 4 (“Tx diversity ornot” in FIG. 4). However, as shown in FIG. 4, indication of theseparameters requires a predetermined number of bits per ePDCCH candidate,and when these parameters are indicated for each ePDCCH candidate, Ntimes the number of bits necessary for one ePDCCH candidate (number ofePDCCH candidate positions, N=32 in FIG. 4, for example) is necessary.

An object of the present invention is to provide a reception apparatus,a transmission apparatus, a reception method and a transmission methodcapable of switching between transmission methods while avoiding anincrease in the number of times blind decoding is performed and theamount of signaling required for indication.

Solution to Problem

A reception apparatus according to an aspect of the present inventionincludes: a reception section that receives a signal mapped to one of aplurality of mapping candidates; and a processing section that performsblind decoding on the plurality of mapping candidates using one of afirst transmission method and a second transmission method in accordancewith an aggregation level configured for each of the plurality ofmapping candidates, the first transmission method using a single antennaport to perform precoding based on feedback information from a receptionapparatus and the second transmission method using multiple antennaports to perform transmission diversity.

A transmission apparatus an aspect of the present invention includes: aprecoding section that performs precoding on a signal mapped to one of aplurality of mapping candidates using one of a first transmission methodand a second transmission method in accordance with an aggregation levelconfigured for each of the plurality of mapping candidates, the firsttransmission method using a single antenna port to perform precodingbased on feedback information from a reception apparatus and the secondtransmission method using multiple antenna ports to perform transmissiondiversity; and a transmission section that transmits the precodedsignal.

A reception method an aspect of the present invention includes:receiving a signal mapped to one of a plurality of mapping candidates;and performing blind decoding on the plurality of mapping candidatesusing one of a first transmission method and a second transmissionmethod in accordance with an aggregation level configured for each ofthe plurality of mapping candidates, the first transmission method usinga single antenna port to perform precoding based on feedback informationfrom a reception apparatus and the second transmission method usingmultiple antenna ports to perform transmission diversity.

A transmission method an aspect of the present invention includes:performing precoding on a signal mapped to one of a plurality of mappingcandidates using one of a first transmission method and a secondtransmission method in accordance with an aggregation level configuredfor each of the plurality of mapping candidates, the first transmissionmethod using a single antenna port to perform precoding based onfeedback information from a reception apparatus and the secondtransmission method using multiple antenna ports to perform transmissiondiversity; and transmitting the precoded signal.

Advantageous Effects of Invention

According to the present invention, it is possible to switch betweentransmission methods while avoiding an increase in the number of timesblind decoding is performed and the amount of signaling required forindication.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram provided for describing a PRB pair;

FIG. 2 illustrates an example of search spaces corresponding toR-PDCCHs;

FIG. 3 illustrates an example of an ePDCCH allocation method;

FIG. 4 illustrates the number of bits necessary to indicate eachtransmission parameter;

FIG. 5 is a block diagram illustrating main components of aconfiguration of a base station according to Embodiment 1 of the presentinvention;

FIG. 6 is a block diagram illustrating main components of a terminalaccording to Embodiment 1 of the present invention;

FIG. 7 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the present invention;

FIG. 8 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 9 illustrates an example of switching between transmission methodsaccording to Embodiment 1 of the present invention (operation example1-1);

FIG. 10 illustrates an example of switching between transmission methodsaccording to Embodiment 1 of the present invention (operation example1-2);

FIG. 11 illustrates an example of switching between transmission methodsaccording to Embodiment 1 of the present invention (operation example1-3);

FIG. 12 illustrates an example of switching between transmission methodsaccording to Embodiment 1 of the present invention (operation example1-3);

FIG. 13 illustrates an example of mapping of antenna ports according toEmbodiment 1 of the present invention;

FIG. 14 illustrates another example of switching between transmissionmethods according to Embodiment 1 of the present invention;

FIG. 15 illustrates an example of switching between transmission methodsaccording to Embodiment 2 of the present invention

FIG. 16 illustrates an example of switching between transmission methodsaccording to Embodiment 3 of the present invention

FIG. 17 is a diagram provided for describing switching betweenconventional transmission methods;

FIG. 18 illustrates an example of switching between transmission methodsaccording to Embodiment 4 of the present invention (operation example4-1);

FIG. 19 illustrates an example of switching between transmission methodsaccording to Embodiment 4 of the present invention (operation example4-2);

FIG. 20 illustrates an example of switching between transmission methodsaccording to Embodiment 5 of the present invention;

FIG. 21 illustrates an example of mapping of antenna ports according toEmbodiment 6 of the present invention; and

FIG. 22 illustrates an example of switching between transmission methodsaccording to Embodiment 6 of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention will be described in detailhereunder with reference to the accompanying drawings. Throughout theembodiments, the same elements are assigned the same reference numerals,and any duplicate description of the elements is omitted.

Embodiment 1

[Communication System Overview]

A communication system according to the present embodiment includes atransmission apparatus and a reception apparatus. In particular, thepresent embodiment is described by taking base station 100 as thetransmission apparatus and taking terminal 200 as the receptionapparatus. The communication system is, for example, an LTE-Advancedsystem. Base station 100 is, for example, a base station that supportsthe LTE-Advanced system, and terminal 200 is, for example, a terminalthat supports the LTE-Advanced system.

FIG. 5 is a block diagram illustrating main components of base station100 according to the present embodiment.

In base station 100, precoding section 105 performs precoding on asignal mapped to one of a plurality of ePDCCH candidates using one offirst transmission method (single antenna port transmission) using oneof a first transmission method (single antenna port transmission) usingsingle antenna port to perform precoding based on feedback informationfrom terminal 200 and a second transmission method (transmissiondiversity using multiple antenna ports) that performs transmissiondiversity using multiple antenna ports in accordance with theaggregation level configured for each of a plurality of ePDCCHcandidates (mapping candidates). Transmission section 107 transmits theprecoded signals.

FIG. 6 is a block diagram illustrating main components of terminal 200according to the present embodiment.

In terminal 200, reception section 201 receives a signal mapped to oneof the plurality of ePDCCH candidates (mapping candidates). Controlsignal processing section 205 performs blind decoding on the pluralityof ePDCCH candidates using one of a first transmission method (singleantenna port transmission) using single antenna port to performprecoding based on feedback information from terminal 200 and a secondtransmission method (transmission diversity using multiple antennaports) that performs transmission diversity using multiple antenna portsin accordance with the aggregation level configured for each of aplurality of ePDCCH candidates (mapping candidates).

[Configuration of Base Station 100]

FIG. 7 is a block diagram illustrating a configuration of base station100 according to the present embodiment. As illustrated in FIG. 7, basestation 100 includes assignment information generation section 101,configuration section 102, error correction coding section 103,modulation section 104, precoding section 105, signal assignment section106, transmission section 107, reception section 108, demodulationsection 109, and error correction decoding section 110.

In a case where there is a downlink data signal (DL data signal) to betransmitted and an uplink data signal (UL data signal) to be assigned toan uplink (UL), assignment information generation section 101 determinesresources (RB) to which the data signals are assigned, and generatesassignment information (DL assignment and UL grant). The DL assignmentincludes information relating to assignment of the DL data signal. TheUL grant includes information relating to allocated resources for the ULdata signal to be transmitted from terminal 200. Assignment informationgeneration section 101 determines a PDCCH candidate number (numberassigned to a mapping candidate in PDCCH) to which the generatedassignment information (DL assignment and UL grant) is assigned or anePDCCH candidate number. The assignment information and PDCCH candidatenumber or ePDCCH candidate number are outputted to signal assignmentsection 106. The DL assignment is outputted to signal assignment section106 as control information for assigning a DL data signal and the ULgrant is outputted to reception section 108 as control information forreceiving a UL data signal.

Configuration section 102 configures a method of transmitting controlsignals transmitted by ePDCCH or PDCCH. For example, configurationsection 102 configures one of single antenna port transmission andtransmission diversity using multiple antenna ports in accordance withan aggregation level configured for each of a plurality of ePDCCHcandidates for ePDCCH. The configured “information relating totransmission method” is outputted to precoding section 105 and alsooutputted to error correction coding section 103 as a control signal.

Error correction coding section 103 receives a transmission data signal(DL data signal) and control information received from configurationsection 102 as input signals, performs error correction coding on theinput signals, and outputs the processed signals to modulation section104.

Modulation section 104 modulates the signals received from errorcorrection coding section 103, and outputs the modulated data signal toprecoding section 105.

Precoding section 105 performs precoding processing on the controlsignals transmitted by ePDCCH or PDCCH. More specifically, for controlsignals, precoding section 105 determines precoding to be used based onthe transmission method (single antenna port transmission ortransmission diversity using multiple antenna ports) indicated fromconfiguration section 102 and the ePDCCH candidate number or PDCCHcandidate number indicated from assignment information generationsection 101. Precoding section 105 then multiplies the control signalsby the determined precoding for each antenna port and outputs theprecoded control signals to signal assignment section 106. Precodingsection 105 also multiplies data signals by precoding defined for eachand outputs the precoded data signals to signal assignment section 106.

Signal assignment section 106 assigns the assignment information (DLassignment and UL grant) received from assignment information generationsection 101 to ePDCCH or PDCCH. Signal assignment section 106 assignsthe data signals received from precoding section 105 to downlinkresources corresponding to the assignment information (DL assignment)received from assignment information generation section 101.

A transmission signal is formed by assignment information and a datasignal being assigned to predetermined resources in this manner. Thethus-formed transmission signal is outputted to transmission section107.

Transmission section 107 executes radio transmission processing such asup-conversion on the input signal, and transmits the obtained signal toterminal 200 via an antenna.

Reception section 108 receives a signal transmitted from terminal 200via an antenna, and outputs the received signal to demodulation section109. More specifically, reception section 108 separates a signal thatcorresponds to a resource indicated by a UL grant received fromassignment information generation section 101 from the received signal,and executes reception processing such as down-conversion on theseparated signal and thereafter outputs the obtained signal todemodulation section 109.

Demodulation section 109 executes demodulation processing on the inputsignal, and outputs the obtained signal to error correction decodingsection 110.

Error correction decoding section 110 decodes the input signal to obtainthe received data signal from terminal 200.

[Configuration of Terminal 200]

FIG. 8 is a block diagram illustrating the configuration of terminal 200according to the present embodiment. As illustrated in FIG. 8, terminal200 includes reception section 201, signal separating section 202,demodulation section 203, error correction decoding section 204, controlsignal processing section 205, error correction coding section 206,modulation section 207, signal assignment section 208, and transmissionsection 209.

Reception section 201 receives a signal transmitted from base station100 via an antenna, and after executing reception processing such asdown-conversion on the received signal, outputs the processed signal tosignal separating section 202. Received signals include, for example,control signals mapped to one of a plurality of ePDCCH candidatesconstituting search spaces in ePDCCH.

Signal separating section 202 extracts a control signal relating toresource allocation from the reception signal received from receptionsection 201, and outputs the extracted signal to control signalprocessing section 205. Signal separating section 202 also extracts fromthe reception signal a signal corresponding to a data resource (that is,a DL data signal and control signal) indicated by the DL assignmentoutputted from control signal processing section 205, and outputs theextracted signal to demodulation section 203.

Demodulation section 203 demodulates the signal outputted from signalseparating section 202, and outputs the demodulated signal to errorcorrection decoding section 204.

Error correction decoding section 204 decodes the demodulated signaloutputted from demodulation section 203, and outputs the obtainedreceived data signal. In particular, error correction decoding section204 outputs “information relating to transmission method” transmitted asa control signal from base station 100, to control signal processingsection 205.

Control signal processing section 205 identifies a transmission method(precoding) configured for each PDCCH candidate or ePDCCH candidatebased on the “information relating to transmission method” indicated inthe information received from error correcting decoding section 204 inthe signal component received from signal separating section 202.Control signal processing section 205 performs blind decoding on eachPDCCH candidate or each ePDCCH candidate using the identifiedtransmission method, and thereby detects a control signal (DL assignmentor UL grant) for terminal 200. For example, control signal processingsection 205 performs blind decoding on a plurality of ePDCCH candidatesusing one of single antenna port transmission and transmission diversityusing multiple antenna ports in accordance with the aggregation levelconfigured for each of the plurality of ePDCCH candidates constitutingsearch spaces in ePDCCH, and thereby obtains a control signal intendedfor terminal 200. Control signal processing section 205 outputs adetected DL assignment intended for terminal 200 to signal separatingsection 202, and outputs a detected UL grant intended for terminal 200to signal assignment section 208.

When a transmission data signal (UL data signal) is inputted to errorcorrection coding section 206, error correction coding section 206performs error correction coding on the transmission data signal andoutputs the obtained signal to modulation section 207.

Modulation section 207 modulates the signal outputted from errorcorrection coding section 206, and outputs the modulated signal tosignal assignment section 208.

Signal assignment section 208 assigns the signal outputted frommodulation section 207 according to the UL grant received from controlsignal processing section 205, and outputs the obtained signal totransmission section 209.

Transmission section 209 executes transmission processing such asup-conversion on the input signal, and transmits the obtained signal.

[Operation of Base Station 100 and Terminal 200]

The operation of base station 100 and terminal 200 each configured inthe manner described above will be described.

The present embodiment uses an aggregation level as a reference forswitching between single antenna port transmission (One Tx port) andtransmission diversity using multiple antenna ports (Tx diversity).

More specifically, in the present embodiment, base station 100 performsprecoding using single antenna port transmission for ePDCCH candidatescorresponding to a low aggregation level and performs precoding usingtransmission diversity using multiple antenna ports for ePDCCHcandidates corresponding to a high aggregation level. On the other hand,terminal 200 receives (blind-decodes) a signal for ePDCCH candidatescorresponding to a low aggregation level assuming single antenna porttransmission and receives (blind-decodes) a signal for ePDCCH candidatescorresponding to a high aggregation level assuming transmissiondiversity using multiple antenna ports.

Thus, the lower the aggregation level configured for a plurality ofePDCCH candidates constituting search spaces in ePDCCH, the greater isthe number of mapping candidates blind-decoded using single antenna porttransmission, and the higher the configured aggregation level, thegreater is the number of mapping candidates blind-decoded usingtransmission diversity using multiple antenna ports.

On the other hand, in this case, there is a limitation that it is hardto use a combination of a low aggregation level and transmissiondiversity using multiple antenna ports and a combination of a highaggregation level and single antenna port transmission.

However, low aggregation levels (e.g., levels 1 and 2 are assumed to beused in cases where reliability of feedback information from terminal200 to base station 100 is relatively high such as when channel qualityis good or when the moving speed of terminal 200 is relatively slow. Forthis reason, for low aggregation levels, single antenna porttransmission is effective in which precoding is selected based onfeedback information.

On the other hand, high aggregation levels (e.g., levels 4 and 8) areassumed to be used in cases where reliability of feedback informationfrom terminal 200 to base station 100 is relatively low such as whenchannel quality is poor or when the moving speed of terminal 200 isrelatively high. For this reason, for high aggregation levels,transmission diversity using multiple antenna ports is effective toobtain a diversity gain.

From above, even if the aforementioned limitation is generated regardinga combination of a transmission method and an aggregation level, theinfluence on ePDCCH reception characteristics is small.

Hereinafter, operation example 1-1 to operation example 1-3 of basestation 100 and terminal 200 according to the present embodiment will bedescribed.

The following description assumes, as an example, that the numbers ofePDCCH candidates (that is, the numbers of blind decoding targets) are12, 12, 4 and 4 for aggregation levels 1, 2, 4 and 8 respectively.

During single antenna port transmission, an antenna port is used whichis indicated beforehand from base station 100 to terminal 200 using ahigher layer control signal. On the other hand, during transmissiondiversity using multiple antenna ports, a transmission diversity method(e.g., transmission diversity using 2 antenna ports) and antenna portsto be used are configured beforehand.

OPERATION EXAMPLE 1-1

In operation example 1-1, base station 100 and terminal 200 apply singleantenna port transmission as the transmission method for ePDCCHcandidates at a low aggregation level and applies transmission diversityusing 2 antenna ports as the transmission method for ePDCCH candidatesat a high aggregation level.

For example, in base station 100, configuration section 102 configuressingle antenna port transmission as the transmission method for ePDCCHcandidates at aggregation levels 1 and 2. On the other hand,configuration section 102 configures transmission diversity using 2antenna ports as the transmission method for ePDCCH candidates ataggregation levels 4 and 8.

Thus, precoding section 105 performs precoding processing on ePDCCHcandidates (ePDCCH candidate numbers: #0 to #23) corresponding toaggregation levels 1 and 2 as shown in FIG. 9 using single antenna porttransmission. On the other hand, precoding section 105 performsprecoding processing on ePDCCH candidates (ePDCCH candidate numbers: #24to #31) corresponding to aggregation levels 4 and 8 using transmissiondiversity using 2 antenna ports.

On the other hand, in terminal 200, control signal processing section205 performs blind decoding on ePDCCH candidates (ePDCCH candidatenumbers: #0 to #23) corresponding to aggregation levels 1 and 2 usingsingle antenna port transmission as shown in FIG. 9. On the other hand,control signal processing section 205 performs blind decoding on ePDCCHcandidates (ePDCCH candidate numbers: #24 to #31) corresponding toaggregation levels 4 and 8 using transmission diversity using 2 antennaports.

Thus, since terminal 200 can identify a transmission method inaccordance with aggregation levels, signaling for switching betweentransmission method is no longer necessary. For example, compared to thecase where the transmission method is indicated for each ePDCCHcandidate as shown in FIG. 4, it is possible to reduce the number ofbits necessary for indicating switching between transmission methods (Txdiversity or not) from N bits (32 bits in FIG. 4) to 0 bits.

In operation example 1-1, it is possible to switch between transmissionmethods for each ePDCCH candidate corresponding to each aggregationlevel at a boundary between specific aggregation levels (betweenaggregation levels 2 and 4 in FIG. 9). Thus, compared to the case whereonly one transmission method can be configured by signaling of a higherlayer such as R-PDCCH, dynamic switching between transmission methods ispossible in ePDCCH.

A case has been described in FIG. 9 where the transmission method isswitched between aggregation levels 1 and 2 (less than predeterminedvalue 4) and aggregation levels 4 and 8 (equal to or above predeterminedvalue 4), but the present invention is not limited to this. For example,signaling indicating a boundary between which aggregation levels shouldbe used as a reference for switching between the transmission methodsmay be transmitted from base station 100 to terminal 200. For example,in the case of “00,” single antenna port transmission may be used ataggregation levels 1 and 2, and transmission diversity using multipleantenna ports may be used at aggregation levels 4 and 8, in the case of“01,” single antenna port transmission may be used at aggregation levels1, 2 and 4 and transmission diversity using multiple antenna ports maybe used at aggregation level 8, in the case of “10,” single antenna porttransmission may be used at aggregation levels 1, 2, 4 and 8 (that is,all levels), and in the case of “11,” transmission diversity usingmultiple antenna ports may be used at aggregation levels 1, 2, 4 and 8(that is, all levels). The amount of signaling necessary for switchingbetween the transmission methods is no more than 2 bits in this casetoo. That is, it is also possible to reduce the number of bits necessaryfor switching between the transmission methods in this case compared tothe method of indicating the transmission method shown in FIG. 4.

Alternatively, in addition to the above-described four patterns, apattern in which single antenna port transmission is used at aggregationlevel 1 and transmission diversity using multiple antenna ports is usedat aggregation levels 2, 4 and 8, may be added, and one of a total offive patterns may be indicated (that is, indicated with 3 bits) frombase station 100 to terminal 200 or one of four patterns obtained byexcluding one from the above-described five patterns may be indicated(that is, indicated with 2 bits) from base station 100 to terminal 200.

Thus, operation using single antenna port transmission for all ePDCCHcandidates and operation using transmission diversity using multipleantenna ports for all ePDCCH candidates are also possible. Therefore,all ePDCCH candidates can be used effectively even when there isterminal 200 or base station 100 that supports only one transmissionmethod (reception method).

OPERATION EXAMPLE 1-2

In operation example 1-2, ePDCCH candidate numbers are assigned, forexample, in ascending order from ePDCCH candidates corresponding to lowaggregation levels to ePDCCH candidates corresponding to highaggregation levels.

For example, as shown in FIG. 10, for 32 ePDCCH candidates, ePDCCHcandidate numbers #0 to #31 are assigned in ascending order from ePDCCHcandidates corresponding to lower aggregation levels. More specifically,as shown in FIG. 10, ePDCCH candidates with ePDCCH candidate numbers #0to #11 correspond to aggregation level 1, ePDCCH candidates with ePDCCHcandidate numbers #12 to #23 correspond to aggregation level 2, ePDCCHcandidates with ePDCCH candidate numbers #24 to #27 correspond toaggregation level 4 and ePDCCH candidates with ePDCCH candidate numbers#28 to #31 correspond to aggregation level 8.

In base station 100, configuration section 102 configures a specificePDCCH candidate number for switching between transmission methods(reference for switching between ePDCCH transmission methods) for eachterminal 200. For example, in FIG. 10, configuration section 102configures ePDCCH candidate number #20 corresponding to aggregationlevel 2 as a reference for switching between ePDCCH transmissionmethods. Configured ePDCCH candidate number #20 (information relating toswitching between ePDCCH transmission methods) is outputted to precodingsection 105. Configured ePDCCH candidate number #20 is also indicated toterminal 200 as a control signal. For example, higher layer signaling isused for this indication.

As shown in FIG. 10, precoding section 105 performs precoding processingon ePDCCH candidates (#0 to #19) assigned ePDCCH candidate numbers lowerthan #20 using single antenna port transmission. On the other hand, asshown in FIG. 10, precoding section 105 performs precoding processing onePDCCH candidates (#20 to #31) assigned ePDCCH candidate numbers equalto or greater than #20 using transmission diversity using multipleantenna ports.

On the other hand, in terminal 200, reception section 201 receivesePDCCH candidate number #20 as information relating to switching betweenePDCCH transmission methods from base station 100. Thus, as shown inFIG. 10, control signal processing section 205 performs blind decodingon ePDCCH candidates (#0 to #19) assigned ePDCCH candidate numbers lowerthan #20 using single antenna port transmission. On the other hand, asshown in FIG. 10, control signal processing section 205 performs blinddecoding on ePDCCH candidates (#20 to #31) assigned ePDCCH candidatenumbers equal to or greater than #20 using transmission diversity usingmultiple antenna ports.

When the total number of ePDCCH candidates is assumed to be N, thenumber of bits necessary for indicating an ePDCCH candidate whichbecomes the above-described reference for switching between transmissionmethods becomes ceil (log₂(N+1)) bits. Function ceil (x) is a functionthat returns a minimum integer equal to or greater than x.

For example, in FIG. 10, since N=32, ceil (log₂(N+1))=6 bits.

Note that, when #N (#32 in FIG. 10) is indicated from base station 100to terminal 200, single antenna port transmission may be adopted as thetransmission method for all ePDCCH candidates, whereas when #0 isindicated, transmission diversity using multiple antenna ports may beadopted as the transmission method for all ePDCCH candidates.

Assuming a range for indicating an ePDCCH candidate which becomes theabove-described reference for switching between transmission methods is#0 to #N−1, when #N−1 (#31 in FIG. 10) is indicated from base station100 to terminal 200, single antenna port transmission may be adopted asthe transmission method for all ePDCCH candidates. In this case, thenumber of bits necessary to indicate an ePDCCH candidate which becomesthe above-described reference for switching between transmission methodsbecomes ceil (log₂(N)) bits. For example, in FIG. 10, since N=32, ceil(log₂(N))=5 bits, which is one bit fewer than ceil (log₂(N+1)).

Thus, by receiving an indication of an ePDCCH candidate number whichbecomes a reference for switching between transmission methods from basestation 100, terminal 200 can identify the transmission method. Thus,compared to the case as shown, for example, in FIG. 4 where atransmission method is indicated for each ePDCCH candidate, it ispossible to reduce the number of bits necessary to indicate switchingbetween transmission methods (Tx diversity or not) from N bits (32 bitsin FIG. 4) to ceil (log₂(N+1)) bits or ceil (log₂(N)) bits (6 bits or 5bits).

In operation example 1-2, operation adopting single antenna porttransmission for all ePDCCH candidates and operation adoptingtransmission diversity using multiple antenna ports for all ePDCCHcandidates are also possible. Thus, even when terminal 200 or basestation 100 that supports only one transmission method (receptionmethod) exists, it is possible to effectively use all ePDCCH candidates.

In operation example 1-2, it is possible to switch between transmissionmethods for each ePDCCH candidate corresponding to each aggregationlevel using an ePDCCH candidate number which becomes a reference forswitching between transmission methods as a boundary. This enablesdynamic switching between transmission methods in ePDCCH compared to thecase where only one transmission method can be configured throughsignaling of a higher layer such as R-PDCCH.

In operation example 1-2, of ePDCCH candidates (#12 to #23)corresponding to aggregation level 2 shown, for example, in FIG. 10,single antenna port transmission is configured for some ePDCCHcandidates (#12 to #19) and transmission diversity using multipleantenna ports is configured for the remaining ePDCCH candidates (#20 to#23). That is, in operation example 1-1, switching between transmissionmethods in units of aggregation levels is possible, whereas in operationexample 1-2, switching between transmission methods in units of ePDCCHcandidates is further possible at specific aggregation levels. Thus, inoperation example 1-2 compared to operation example 1-1, it is possibleto more flexibly assign control signals to terminal 200.

OPERATION EXAMPLE 1-3

In operation example 1-3, ePDCCH candidate numbers are assigned inascending order from ePDCCH candidates corresponding to aggregationlevels lower than L to ePDCCH candidates corresponding to aggregationlevels equal to or higher than L. L is any given natural number. Theaggregation levels lower than L and aggregation levels equal to orhigher than L may include a plurality of aggregation levels.

For example, as shown in FIG. 11, for 32 ePDCCH candidates, ePDCCHcandidate numbers #0 to #31 are assigned in ascending order from ePDCCHcandidates corresponding to aggregation levels lower than L. Morespecifically, as shown in FIG. 11, ePDCCH candidates with ePDCCHcandidate numbers #0 to #23 correspond to aggregation levels lower thanL (Level<L) and ePDCCH candidates with ePDCCH candidate numbers #24 to#31 correspond to aggregation levels equal to or higher than L(Level≧L).

In base station 100, configuration section 102 configures a specificePDCCH candidate number for switching between transmission methods(reference for switching between transmission methods of ePDCCH) foreach terminal 200.

For example, as shown in FIG. 11, a case will be described whereconfiguration section 102 configures ePDCCH candidate number #20corresponding to an aggregation level lower than L as a reference forswitching between transmission methods of ePDCCH. Configured ePDCCHcandidate number #20 (information relating to switching betweentransmission methods of ePDCCH) is outputted to precoding section 105.Moreover, configured ePDCCH candidate number #20 is indicated toterminal 200 as a control signal.

For this indication, for example, signaling of a higher layer is used.

As shown in FIG. 11, precoding section 105 performs precoding processingon ePDCCH candidates (#0 to #19) assigned ePDCCH candidate numbers lowerthan #20 using single antenna port transmission. On the other hand, asshown in FIG. 11, precoding section 105 performs precoding processing onePDCCH candidates (#20 to #31) assigned ePDCCH candidate numbers equalto or greater than #20 using transmission diversity using multipleantenna ports.

On the other hand, in terminal 200, reception section 201 receivesePDCCH candidate number #20 as information relating to switching betweentransmission methods of ePDCCH from base station 100. Thus, controlsignal processing section 205 performs blind decoding on ePDCCHcandidates (#0 to #19) assigned ePDCCH candidate numbers lower than #20as shown in FIG. 11 using single antenna port transmission. On the otherhand, control signal processing section 205 performs blind decoding onePDCCH candidates (#20 to #31) assigned ePDCCH candidate numbers equalto or greater than #20 as shown in FIG. 11 using transmission diversityusing multiple antenna ports.

Next, as shown in FIG. 12, a case will be described where configurationsection 102 configures ePDCCH candidate number #28 corresponding to anaggregation level equal to or greater than L as a reference forswitching between transmission methods of ePDCCH. Configured ePDCCHcandidate number #28 (information relating to switching betweentransmission methods of ePDCCH) is outputted to precoding section 105and indicated to terminal 200 as a control signal.

As shown in FIG. 12, precoding section 105 performs precoding processingon ePDCCH candidates (#0 to #27) assigned ePDCCH candidate numbers lowerthan #28 using single antenna port transmission. On the other hand,precoding section 105 performs precoding processing on ePDCCH candidates(#28 to #31) assigned ePDCCH candidate numbers equal to or greater than#28 as shown in FIG. 12 using transmission diversity using multipleantenna ports.

On the other hand, in terminal 200, reception section 201 receivesePDCCH candidate number #28 as information relating to switching betweentransmission methods of ePDCCH from base station 100. Thus, as shown inFIG. 12, control signal processing section 205 performs blind decodingon ePDCCH candidates (#0 to #27) assigned ePDCCH candidate numbers lowerthan #28 using single antenna port transmission. On the other hand, asshown in FIG. 12, control signal processing section 205 performs blinddecoding on ePDCCH candidates (#28 to #31) assigned ePDCCH candidatenumbers equal to or greater than #28 using transmission diversity usingmultiple antenna ports.

Here, when the total number of ePDCCH candidates is assumed to be N, thenumber of bits necessary to indicate an ePDCCH candidate which becomesthe above-described reference for switching between transmission methodscan be ceil (log₂(N+1)) bits or ceil (log₂(N)) bits as in the case ofoperation example 1-2.

In operation example 1-3, it is possible to flexibly switch betweentransmission methods for each ePDCCH candidate using the ePDCCHcandidate number which becomes the reference for switching betweentransmission methods as a boundary. This enables dynamic switchingbetween transmission methods in ePDCCH compared to the case where onlyone transmission method can be configured by higher layer signaling asin the case of R-PDCCH.

In operation example 1-3, among ePDCCH candidates (#0 to #23)corresponding to aggregation levels lower than L shown, for example, inFIG. 11, single antenna port transmission is configured for some ePDCCHcandidates (#0 to #19) and transmission diversity using multiple antennaports is configured for the remaining ePDCCH candidates (#20 to #23).That is, when a plurality of aggregation levels are included inaggregation levels lower than L, both single antenna port transmissionand transmission diversity using multiple antenna ports can also beconfigured at a plurality of aggregation levels.

In operation example 1-3, among ePDCCH candidates (#24 to #31)corresponding to aggregation levels higher than L shown in, for example,FIG. 12, single antenna port transmission is configured for some ePDCCHcandidates (#24 to #27) and transmission diversity using multipleantenna ports is configured for the remaining ePDCCH candidates (#28 to#31). That is, when a plurality of aggregation levels are included inaggregation levels equal to or higher than L, both single antenna porttransmission and transmission diversity using multiple antenna ports canalso be configured at a plurality of aggregation levels.

Here, a case has been described where ePDCCH candidates are divided intoePDCCH candidates corresponding to aggregation levels lower than L andePDCCH candidates corresponding to aggregation levels equal to or higherthan L, but ePDCCH candidates may also be divided into ePDCCH candidatescorresponding to aggregation levels equal to or lower than L and ePDCCHcandidates corresponding to aggregation levels higher than L.

Operation example 1-1 to operation example 1-3 of base station 100 andterminal 200 according to the present embodiment have been described sofar.

Thus, in the present embodiment, base station 100 and terminal 200 usesingle antenna port transmission for ePDCCH candidates corresponding tolow aggregation levels and use transmission diversity using multipleantenna ports for ePDCCH candidates corresponding to high aggregationlevels. This allows terminal 200 to identify a transmission method inaccordance with an aggregation level configured in each ePDCCHcandidate. That is, the amount of signaling required to indicate atransmission method can be reduced compared to the case where atransmission method is indicated for each ePDCCH candidate.

Regarding a plurality of ePDCCH candidates making up a search space inePDCCH, the lower the configured aggregation level, the more ePDCCHcandidates are precoded (blind decoded) using single antenna porttransmission. On the other hand, the higher the configured aggregationlevel, the more ePDCCH candidates are precoded (blind decoded) usingtransmission diversity using multiple antenna ports. That is, basestation 100 and terminal 200 can switch, in accordance with anaggregation level configured in each ePDCCH candidate, the transmissionmethod to one appropriate to the aggregation level.

Thus, according to the present embodiment, it is possible to dynamicallyswitch between transmission methods while avoiding an increase in thenumber of times blind decoding is performed in terminal 200 and anincrease in the amount of signaling required to indicate a transmissionmethod.

In the present embodiment, in order to enable uniquely identifying ofantenna ports for transmission diversity using multiple antenna portsfrom antenna ports for single antenna port transmission indicated foreach terminal 200, antenna ports to be used for both transmissionmethods may be associated with each other in advance. For example, FIG.13 illustrates association between antenna ports for single antenna porttransmission and antenna ports for transmission diversity using twoantenna ports. In FIG. 13, base station 100 indicates 2-bit information(00, 01, 10, 11) to terminal 200, and terminal 200 can thereby uniquelyidentify antenna ports to be used for both transmission methods. Asantenna ports for transmission diversity using two antenna ports,combinations of ports #7 and #9, and ports #8 and #10 may also be used.For example, while 3 bits (2 bits (4 types)+1 bit (2 types)) arenecessary when antenna ports used for each transmission method areindividually indicated, in FIG. 13, 2 bits are necessary, and thereforethe number of bits can be reduced by 1 bit. Alternatively, only the sameantenna ports (e.g., ports #7, #8, ports #9, #10 or ports #7, #9) may beconfigured beforehand to be always used as antenna ports fortransmission diversity using multiple antenna ports.

A case has been described in the present embodiment where 32 ePDCCHcandidates are used as shown, for example, in FIG. 9 and FIG. 10, butthe number of ePDCCH candidates is not limited to 32. All of the ePDCCHcandidates as targets of switching between transmission methods may be,for example, a region to which control information relating to downlink(DL) is mapped or a region to which control information relating touplink (UL) is mapped or a region in which the regions to which controlinformation relating to downlink (DL) and control information relatingto uplink (UL) are mapped are mixed. For example, for each ofaggregation levels 1, 2, 4 and 8, the number of ePDCCH candidatescorresponding to downlink control information may be set to 6, 6, 2 and2 respectively and the number of ePDCCH candidates corresponding touplink control information may be set to 6, 6, 2 and 2 respectively. Thetotal number of ePDCCH candidates is also 32 as in the cases of FIG. 9and FIG. 10 in this case, too.

In the present embodiment, an ePDCCH candidate for switching betweentransmission methods is indicated using 2 bits in operation example 1-1and ceil (log₂(N+1)) bits or ceil (log₂(N)) bits in operation example1-2 and operation example 1-3, but the present invention is not limitedto this. For example, assuming that the number of indication bits is K,positions at which the number of ePDCCH candidates is divided by(2^(K)−1) may be indicated. FIG. 14 illustrates an example of K=3 (acase where the number of ePDCCH candidates is divided by 7). As shown inFIG. 14, eight types of switching indication signals 0 to 7 arerepresented by 3 bits. As shown in FIG. 14, when the switchingindication signal is 0, transmission diversity (Tx diversity) of aplurality of antennas is configured for all ePDCCH candidates, and whenthe switching indication signal is 7, single antenna port transmission(One Tx port) is configured for all ePDCCH candidate positions. When theswitching indication signal shown in FIG. 14 is one of 1 to 6, singleantenna port transmission is configured for ePDCCH candidates assigned anumber less than the ePDCCH candidate number of the ePDCCH candidate(switching candidate position) corresponding to the switching indicationsignal, and transmission diversity of a plurality of antennas isconfigured for ePDCCH candidates assigned numbers equal to or greaterthan the ePDCCH candidate number of the switching candidate position.The ePDCCH candidates (switching candidate positions) corresponding toswitching indication signals 1 to 6 shown in FIG. 14 may be determinedbeforehand by higher layer signaling or determined through calculations.As an example of the case where the ePDCCH candidates are determinedthrough calculations, an ePDCCH candidate corresponding to eachswitching indication signal may be calculated asRound(((N+1)/(2^(K)−1))*value of switching indication signal). FunctionRound(x) returns a value obtained by rounding off x to the nearestinteger. For example, if N=32 and K=3 are assumed, switching indicationsignal 1 becomes ePDCCH candidate position #5, switching indicationsignal 2 becomes ePDCCH candidate position #9, switching indicationsignal 3 becomes ePDCCH candidate position #14, switching indicationsignal 4 becomes ePDCCH candidate position #19, switching indicationsignal 5 becomes ePDCCH candidate position #24, and switching indicationsignal 6 becomes ePDCCH candidate position #28. By so doing, the numberof bits can be reduced compared to the case where ceil (log₂(N+1)) bitsare used.

The ePDCCH candidates (e.g., 32 ePDCCH candidates shown in FIG. 9 andFIG. 10) as targets of switching between transmission methods may beregions making up search spaces specific to terminal 200 (UE specificSearch Space: UE-SS) or regions making up search spaces common to aplurality of terminals 200 (Common Search Space: C-SS) or a region inwhich regions making up UE-SS and C-SS respectively are mixed.

Embodiment 2

A case has been described in Embodiment 1 where the number of ePDCCHcandidates corresponding to each aggregation level is configuredbeforehand. In contrast, a case will be described in the presentembodiment where the number of ePDCCH candidates corresponding to eachaggregation level is selected from among a plurality of candidates.

A base station and a terminal according to the present embodiment havebasic configurations common to those of base station 100 and terminal200 according to Embodiment 1, and therefore their basic configurationswill be described with reference to FIGS. 7 and 8.

One of operation example 1-1 and operation example 1-2 of Embodiment 1may be applied to switching between transmission methods in the presentembodiment and description thereof will be omitted here.

For example, as shown in FIG. 15, as in the case of operation example1-2 of Embodiment 1, for 32 ePDCCH candidates as shown in FIG. 15,ePDCCH candidate numbers #0 to #31 are assigned in ascending order fromePDCCH candidates corresponding to lower aggregation levels. However,the configuration of an aggregation level corresponding to each ePDCCHcandidate is variable.

In base station 100, configuration section 102 configures ePDCCHcandidates whose aggregation levels are switched. More specifically,configuration section 102 configures corresponding ePDCCH candidates ata switching position between aggregation levels 1 and 2, a switchingposition between aggregation levels 2 and 4, and a switching positionbetween aggregation levels 4 and 8 respectively. For example, in FIG.15, configuration section 102 configures ePDCCH candidate number #6 as astart position of aggregation level 2 (corresponding to the position ofswitching between aggregation levels 1 and 2). In FIG. 15, configurationsection 102 configures ePDCCH candidate number #18 as a start positionof aggregation level 4 (corresponding to the position of switchingbetween aggregation levels 2 and 4). Likewise, in FIG. 15, configurationsection 102 configures ePDCCH candidate number #26 as a start positionof aggregation level 8 (corresponding to the position of switchingbetween aggregation levels 4 and 8)

Configuration section 102 then outputs information indicating ePDCCHcandidates (#6, #18 and #26) corresponding to the positions of switchingbetween different aggregation levels to error correction coding section103. This causes the information to be indicated to terminal 200.

On the other hand, in terminal 200, reception section 201 receivesinformation indicating ePDCCH candidates (#6, #18 and #26) correspondingto the positions of switching between different aggregation levels.Control signal processing section 205 then configures an aggregationlevel for each of a plurality of ePDCCH candidates (#0 to #31) based oninformation indicating ePDCCH candidates (#6, #18 and #26) correspondingto the positions of switching between different aggregation levels.

By so doing, in base station 100 and terminal 200, as shown in FIG. 15,ePDCCH candidate numbers #0 to #5 are configured for aggregation level1, ePDCCH candidate numbers #6 to #17 are configured at aggregationlevel 2, ePDCCH candidate numbers #18 to #25 are configured ataggregation level 4, and ePDCCH candidate numbers #26 to #31 areconfigured at aggregation level 8.

Here, the total number of ePDCCH candidates is assumed to be N andaggregation levels are assumed to be 1, 2, 4 and 8, and since switchingbetween aggregation levels is indicated by three ePDCCH candidatenumbers, the number of bits necessary for indication is 3*ceil(log₂(N+1)) bits. For example, in FIG. 15, N=32 and therefore 3*ceil(log₂(N+1))=18 bits.

Note that when #N (#32 in FIG. 15) is indicated with all three ePDCCHcandidate numbers from base station 100 to terminal 200, aggregationlevels may be assumed to be 1 for all ePDCCH candidates, and when #0 isindicated with all three ePDCCH candidate numbers, aggregation levelscorresponding to all ePDCCH candidates may be assumed to be 8.

When a range of indicating ePDCCH candidates indicating switchingbetween aggregation levels is assumed to be #0 to #N−1 and #N−1 (#31 inFIG. 15) is indicated from base station 100 to terminal 200, aggregationlevels corresponding to all ePDCCH candidates may be assumed to be 8. Inthis case, the number of bits necessary to indicate switching betweenaggregation levels is 3*ceil (log₂(N)) bits. For example, in FIG. 15,since N=32, 3*ceil (log₂(N))=15 bits, and the number of bits is reducedby 3 bits compared to the case with 3*ceil (log₂(N+1)).

Thus, terminal 200 identifies an aggregation level configured in eachePDCCH candidate by being indicated by the base station of the ePDCCHcandidate number corresponding to the position of switching betweenaggregation levels. Thus, compared to the case as shown in FIG. 4 wherethe transmission method is indicated for each ePDCCH candidate, it ispossible to reduce the number of bits necessary to indicate aggregationlevels from 2*N bits (64 bits in FIG. 4) to 3*ceil (log₂(N+1)) bits or3*ceil (log₂(N)) bits (18 bits or 15 bits).

For a plurality of ePDCCH candidates making up search spaces in ePDCCH,base station 100 may configure an ePDCCH candidate number correspondingto the position of switching between different aggregation levels to bevariable. For example, base station 100 may configure ePDCCH candidatenumbers corresponding to the position of switching between differentaggregation levels so that the ratio of the number of ePDCCH candidatescorresponding to aggregation levels more frequently used to the totalnumber of a plurality of ePDCCH candidates is higher. For example, whenthe number of REs is high, the number of ePDCCH candidates correspondingto low aggregation levels may be increased and when the number of REs issmall, the number of ePDCCH candidates corresponding to high aggregationlevels may be increased. In this way, it is possible to reduce thenumber of ePDCCH candidates corresponding to aggregation levels lessfrequently used and increase the number of ePDCCH candidatescorresponding to aggregation levels more frequently used. That is, adegree of freedom can be provided in the selection of the numbers ofePDCCH candidates making up aggregation levels 1, 2, 4 and 8respectively. Thus, base station 100 and terminal 200 can configure anaggregation level appropriate for each cell or terminal 200 withoutchanging the total number of ePDCCH candidates and reduce a probabilityof collision of ePDCCH candidates among a plurality of terminals 200.

Embodiment 3

The present embodiment will describe a case where search spaces similarto shared search spaces (common search spaces: C-SS) in PDCCH areconfigured in ePDCCH.

In the following description, a search space in ePDCCH is called “eC-SS(enhanced common search space)” to be distinguished from C-SS of PDCCH.

As in the case of C-SS of PDCCH, configuration of eC-SS of ePDCCH hastwo applications: (1) to effectively use resource regions by sharingsearch spaces of control signals received individually by terminals (UE)and (2) to transmit/receive control signals (e.g., system information,paging) received in common among terminals.

In above-described application (1), control signals intended forindividual terminals are mapped to ePDCCH candidates in eC-SS.Therefore, when a certain terminal does not use any ePDCCH region, it ispossible to effectively use resources by allocating the ePDCCH region toother terminals. In above-described application (1), antenna ports maybe shared among a plurality of terminals. Therefore, when multipleantenna ports for transmission diversity are configured in eachterminal, multiplexing among terminals becomes easier. Thus,transmission diversity using multiple antenna ports is effective forabove-described application (1).

In above-described application (2), common control signals for aplurality of terminals are mapped to ePDCCH candidates in eC-SS. Forthis reason, it is necessary to relatively improve receiving quality ofePDCCH so as to allow a plurality of terminals to receive signals. Thus,in above-described application (2), only high aggregation levels (e.g.,levels 4 and 8) may be used in eC-SS. Thus, transmission diversity usingmultiple antenna ports is also effective for above-described application(2) to obtain a diversity gain for high aggregation levels (e.g., levels4 and 8).

Thus, in the present embodiment, eC-SS is configured in ePDCCH such thatmore ePDCCH candidates to be precoded (blind-decoded) using transmissiondiversity using multiple antenna ports are configured.

Note that a base station and a terminal according to the presentembodiment have basic configurations common to those of base station 100and terminal 200 according to Embodiment 1, and therefore theirconfigurations will be described with reference to FIGS. 7 and 8.

Hereinafter, operation example 3-1 and operation example 3-2 of basestation 100 and terminal 200 according to the present embodiment will bedescribed.

OPERATION EXAMPLE 3-1

In operation example 3-1, transmission diversity using multiple antennaports is configured as a transmission method for ePDCCH candidatescorresponding to eC-SS irrespective of aggregation levels.

By so doing, terminal 200 can identify a transmission method withoutadditional signaling for the transmission method. For example, even whensingle antenna port transmission is configured in search spaces (UE-SS)specific to terminal 200, terminal 200 can configure transmissiondiversity using multiple antenna ports in eC-SS.

OPERATION EXAMPLE 3-2

In operation example 3-2 as well as operation example 1-2 of Embodiment1, ePDCCH candidate numbers are assigned in ascending order from ePDCCHcandidates corresponding to low aggregation levels to ePDCCH candidatescorresponding to high aggregation levels.

However, ePDCCH candidates corresponding to eC-SS are assigned numbershigher than ePDCCH candidate numbers corresponding to UE-SS.

The following description assumes, as an example, that as shown in FIG.16, the numbers of ePDCCH candidates for aggregation levels 1, 2, 4 and8 of UE-SS are 12, 12, 4 and 4 respectively, and the numbers of ePDCCHcandidates for aggregation levels 4 and 8 of eC-SS are 8 and 4respectively. That is, in FIG. 16, the plurality of ePDCCH candidatesconstituting search spaces in ePDCCH are composed of 32 ePDCCHcandidates in UE-SS and 12 ePDCCH candidates in eC-SS, and the totalnumber of ePDCCH candidates is 44. Control signals specific to terminal200 are mapped to UE-SS. On the other hand, common control signals for aplurality of terminals 200 or control signals specific to terminal 200are mapped to eC-SS.

In this case, as shown in FIG. 16, 32 UE-SS ePDCCH candidates areassigned ePDCCH candidate numbers #0 to #31 in ascending order fromePDCCH candidates corresponding to low aggregation levels. Morespecifically, as shown in FIG. 16, ePDCCH candidate numbers #0 to #11correspond to UE-SS aggregation level 1, ePDCCH candidate numbers #12 to#23 correspond to UE-SS aggregation level 2, ePDCCH candidate numbers#24 to #27 correspond to UE-SS aggregation level 4, and ePDCCH candidatenumbers #28 to #31 correspond to UE-SS aggregation level 8.

As shown in FIG. 16, 12 eC-SS ePDCCH candidates are assigned ePDCCHcandidate numbers #32 to #43 higher than the maximum number assigned toan ePDCCH candidate included in UE-SS (ePDCCH candidate number #31) inascending order from ePDCCH candidates corresponding to loweraggregation levels. More specifically, as shown in FIG. 16, ePDCCHcandidate numbers #32 to #38 correspond to eC-SS aggregation level 4 andePDCCH candidate numbers #40 to #43 correspond to eC-SS aggregationlevel 8.

Here, as shown in FIG. 16, as in the case of operation example 1-2 ofEmbodiment 1, a case will be described where ePDCCH candidate number #26corresponding to UE-SS aggregation level 4 is indicated from basestation 100 to terminal 200 as an ePDCCH candidate number for switchingbetween transmission methods (reference for switching betweentransmission methods of ePDCCH).

In this case, in base station 100, precoding section 105 performsprecoding processing on ePDCCH candidates (#0 to #25) assigned ePDCCHcandidate numbers lower than #26 as shown in FIG. 16 using singleantenna port transmission and performs precoding processing on ePDCCHcandidates (#26 to #43) assigned ePDCCH candidate numbers equal to orhigher than #26 using transmission diversity using 2 antenna ports.

On the other hand, in terminal 200, reception section 201 receivesePDCCH candidate number #26 as information relating to switching betweentransmission methods of ePDCCH from base station 100. Thus, as shown inFIG. 16, control signal processing section 205 performs blind decodingon ePDCCH candidates (#0 to #25) assigned ePDCCH candidate numbers lowerthan #26 using single antenna port transmission and performs blinddecoding on ePDCCH candidates (#26 to #43) assigned ePDCCH candidatenumbers equal to or higher than #26 using transmission diversity using 2antenna ports.

Here, if the total number of ePDCCH candidates is assumed to be N, thenumber of bits necessary to indicate an ePDCCH candidate which becomesthe above-described reference for switching between transmission methodsis ceil (log₂(N+1)) bits. For example, since N=44 in FIG. 16, ceil(log₂(N+1))=6 bits.

As in the case of operation example 1-2 of Embodiment 1, when #N (#44 inFIG. 16) is indicated from base station 100 to terminal 200, singleantenna port transmission may be adopted as the transmission method forall ePDCCH candidates and when #0 is indicated, transmission diversityusing multiple antenna ports may be adopted as the transmission methodfor all ePDCCH candidates.

As in the case of operation example 1-2 of Embodiment 1, if the range ofindication of an ePDCCH candidate which becomes the above-describedreference for switching between transmission methods is assumed to be #0to #N−1 and #N−1 (#43 in

FIG. 16) is indicated from base station 100 to terminal 200, singleantenna port transmission may be adopted as the transmission method forall ePDCCH candidates. In this case, the number of bits necessary toindicate the ePDCCH candidate which becomes the above-describedreference for switching between transmission methods is ceil (log₂(N))bits. For example, since N=44 in FIG. 16, ceil (log₂(N))=6 bits.

Thus, as in the case of Embodiment 1, terminal 200 can identify atransmission method by being indicated from base station 100 of theePDCCH candidate number which becomes a reference for switching betweentransmission methods. Thus, compared to the case shown in FIG. 4 wherethe transmission method is indicated for each ePDCCH candidate, it ispossible to reduce the number of bits necessary to indicate switchingbetween transmission methods (Tx diversity or not) from N bits (here,N=44 bits) to ceil (log₂(N+1)) bits or ceil (log₂(N)) bits (6 bits inFIG. 16).

As shown in FIG. 16, by assigning higher numbers than ePDCCH candidates(#0 to #31) corresponding to UE-SS to ePDCCH candidates (#32 to #43)corresponding to eC-SS, base station 100 and terminal 200 can moreeasily apply transmission diversity using multiple antenna ports toePDCCH candidates corresponding to eC-SS. For this reason, it ispossible to obtain diversity gains with eC-SS and carry outcommunication appropriate for above-described application (2).

Depending on the configuration of a ePDCCH candidate number whichbecomes a reference for switching between transmission methods, it isalso possible to switch between single antenna port transmission andtransmission diversity using multiple antenna ports using one of ePDCCHcandidates corresponding to eC-SS. For example, FIG. 16 corresponds to acase where one of #33 to #42 is configured as an ePDCCH candidate numberwhich becomes a reference for switching between transmission methods.

In this case, transmission by precoding in accordance with feedback(that is, single antenna port transmission) is applicable to some ePDCCHcandidates of eC-SS. Thus, some ePDCCH candidates of eC-SS can be usedas UE-SS and communication appropriate for above-described application(1) is possible.

Thus, for example, base station 100 can switch between the number ofePDCCH candidates used as search spaces specific to terminal 200 and thenumber of ePDCCH candidates used as common search spaces among terminalsin eC-SS in accordance with the number of terminals in a cell or acommunication situation.

In the present embodiment, as in the case of operation example 1 ofEmbodiment 1, when ePDCCH candidate numbers are assigned in ascendingorder from ePDCCH candidates corresponding to aggregation levels lowerthan L (L is a natural number) to ePDCCH candidates corresponding toaggregation levels equal to or higher than L, numbers may be assigned inascending order from mapping candidates corresponding to aggregationlevels lower than L for ePDCCH candidates of UE-SS and ePDCCH candidatenumbers may be assigned in ascending order from a maximum numberassigned to an ePDCCH candidate included in UE-SS for ePDCCH candidatesof eC-SS.

Embodiment 4

The present embodiment uses a method of allocating ePDCCHs (localizedallocation and distributed allocation) as a reference for switchingbetween single antenna port transmission (One Tx port) and transmissiondiversity using multiple antenna ports (Tx diversity).

Note that a base station and a terminal according to the presentembodiment have basic configurations common to those of base station 100and terminal 200 according to Embodiment 1, and therefore theirconfigurations will be described with reference to FIGS. 7 and 8.

As described above, localized allocation is an allocation method toobtain a frequency scheduling gain and can allocate ePDCCHs to resourcesof good channel quality based on channel quality information. On theother hand, distributed allocation can distribute ePDCCHs on thefrequency axis and obtain a frequency diversity gain. That is, bothlocalized allocation and single antenna port transmission have an effectof improving receiving quality for one terminal (UE), and bothdistributed allocation and transmission diversity using multiple antennaports have an effect of stabilizing receiving quality. That is,localized allocation and single antenna port transmission are morelikely to be used for when reliability of feedback information isrelatively high, whereas distributed allocation and transmissiondiversity using multiple antenna ports are more likely to be used forwhen reliability of feedback information is relatively low.

Thus, as shown in FIG. 17, a related art proposes to apply singleantenna port transmission as the transmission method using ePDCCH inlocalized allocation, and apply transmission diversity using multipleantenna ports as the transmission method using ePDCCH in distributedallocation (e.g., see NPL 4).

The present embodiment will describe a method using a combination ofallocation method and transmission method to allow control signals to bemore flexibly allocated from base station 100 to terminal 200.

Hereinafter, operation examples 4-1 and 4-2 of base station 100 andterminal 200 according to the present embodiment will be described.

OPERATION EXAMPLE 4-1

In operation example 4-1, base station 100 indicates, to terminal 200,an ePDCCH candidate for switching between allocation methods of ePDCCHand an ePDCCH candidate for switching between transmission methods. Asshown in FIG. 18, 32 ePDCCH candidates will be described below.

For example, in base station 100, configuration section 102 configuresePDCCH candidate number #22 as a reference for switching betweentransmission methods of ePDCCH. Configuration section 102 alsoconfigures ePDCCH candidate number #19 as a reference for switchingbetween allocation methods of ePDCCH. Configured ePDCCH candidatenumbers #22 and #19 are indicated as control signals to terminal 200.For example, higher layer signaling is used for this indication.

As shown in FIG. 18, precoding section 105 performs precoding processingon ePDCCH candidates (#0 to #21) assigned ePDCCH candidate numbers lowerthan #22 using single antenna port transmission and performs precodingprocessing on ePDCCH candidates (#22 to #31) assigned ePDCCH candidatenumbers equal to or higher than #22 using transmission diversity usingmultiple antenna ports. On the other hand, as shown in

FIG. 18, signal assignment section 106 allocates control signals toresources for ePDCCH candidates (#0 to #18) assigned ePDCCH candidatenumbers lower than #19 using localized allocation, and allocates controlsignals to resources for ePDCCH candidates (#19to #31) assigned ePDCCHcandidate numbers equal to or higher than #19 using distributedallocation.

On the other hand, in terminal 200, control signal processing section205 receives ePDCCH candidate number #22 as information relating toswitching between transmission methods of ePDCCH from base station 100and receives ePDCCH candidate number #19 as information relating toswitching between allocation methods of ePDCCH.

Thus, as shown in FIG. 18, control signal processing section 205performs blind decoding on ePDCCH candidate numbers #0 to #18 assumingsingle antenna port transmission and localized allocation. On the otherhand, as shown in FIG. 18, control signal processing section 205performs blind decoding on ePDCCH candidate numbers #19 to #21 assumingsingle antenna port transmission and distributed allocation. As shown inFIG. 18, control signal processing section 205 performs blind decodingon ePDCCH candidate numbers #22 to #31 assuming transmission diversityusing multiple antenna ports and distributed allocation.

Here, when the total number of ePDCCH candidates is assumed to be N, thenumber of bits necessary to indicate an ePDCCH candidate which becomes areference for switching between transmission methods and an ePDCCHcandidate which becomes a reference for switching between allocationmethods is 2*ceil (log₂(N+1)) bits. For example, since N=32 in FIG. 18,2*ceil (log₂(N+1))=12bits.

Note that when #N (#32 in FIG. 10) is indicated from base station 100 toterminal 200 as a transmission method or allocation method, singleantenna port transmission or localized allocation may be adopted as atransmission method for all ePDCCH candidates, and when #0 is indicated,transmission diversity using multiple antenna ports or distributedallocation may be adopted as a transmission method for all ePDCCHcandidates.

In this way, terminal 200 can identify a transmission method by beingindicated from base station 100 of ePDCCH candidate numbers which becomereferences for switching between the transmission method and allocationmethod. For example, compared to a case where a transmission method isindicated for each ePDCCH candidate as shown in FIG. 4, it is possibleto reduce the number of bits necessary to indicate switching betweentransmission methods (Tx diversity or not) from N bits (32 bits in FIG.4) to ceil (log₂(N+1)) bits (6 bits in FIG. 18). Similarly, compared toa case where an allocation method is indicated for each ePDCCH candidateas shown in FIG. 4, it is possible to reduce the number of bitsnecessary to indicate switching between allocation methods (localized ordistributed) from N bits (32 bits in FIG. 18) to ceil (log₂(N+1)) bits(6 bits in FIG. 18).

Among a plurality of ePDCCH candidates making up search spaces inePDCCH, ePDCCH candidates corresponding to localized allocation are morelikely to be precoded (blind decoded) using single antenna porttransmission and ePDCCH candidates corresponding to distributedallocation are more likely to be precoded (blind decoded) usingtransmission diversity using multiple antenna ports. That is, basestation 100 and terminal 200 can select, according to the allocationmethod configured for each ePDCCH candidate, a transmission methodappropriate for the allocation method. That is, the present embodimentcan improve receiving quality of ePDCCH by securing more ePDCCHcandidates for which a combination of single antenna port transmissionand localized allocation or a combination of transmission diversityusing multiple antenna ports and distributed allocation.

When the related art (FIG. 17) is compared with operation example 4-1(FIG. 18), as shown in FIG. 17, the related art can apply only acombination of localized allocation and single antenna porttransmission, and a combination of distributed allocation andtransmission diversity using multiple antenna ports. In contrast, inoperation example 4-1, a combination of distributed allocation andsingle antenna port transmission (see FIG. 18), and a combination (notshown) of localized allocation and transmission diversity using multipleantenna ports are also supported. Thus, it is possible to more flexiblyallocate control signals from base station 100 to terminal 200.

For example, when feedback information including average CQI (ChannelQuality Indicator: channel quality information) of a whole band and PMI(Precoding Matrix Indicator) of a whole band is fed back from terminal200, a combination of distributed allocation and single antenna porttransmission (ePDCCH candidate numbers #19 to #21 shown in FIG. 18) iseffective. In this case, to acquire CQI of the whole band, sincelocalized allocation whereby a frequency scheduling gain can be obtainedcannot be selected, single antenna port transmission is applied wherebybetter precoding is selected from PMI while performing distributedallocation. For example, in the case of transmission diversity usingmultiple antenna ports, distributed allocation may be always configured.This can be done, for example, by configuring an ePDCCH candidate numberwhich becomes a reference for switching between transmission methods tobe higher than an ePDCCH candidate number which becomes a reference forswitching between allocation methods. In this way, the combination ofdistributed allocation and single antenna port transmission can besecured.

For example, by localized allocation in a certain terminal anddistributed allocation using transmission diversity in other terminals(UEs), when signals of both sides are mapped to the same RB pair,antenna ports can be shared among a plurality of terminals, andtherefore a combination of localized allocation and transmissiondiversity using multiple antenna ports is effective.

In operation example 4-1, it is also possible to adopt operation inwhich single antenna port transmission or localized allocation isconfigured for all ePDCCH candidates and operation in which transmissiondiversity using multiple antenna ports or distributed allocation isconfigured for all ePDCCH candidates. Thus, all ePDCCH candidates can beeffectively used even when there is terminal 200 or base station 100that supports only one transmission method or allocation method.

Furthermore, in operation example 4-1, a transmission method and anallocation method can be switched for each ePDCCH candidate using ePDCCHcandidate numbers which become references for switching betweentransmission methods and between allocation methods as boundaries. Inthis way, compared to the case where only one transmission method or oneallocation method can be configured by higher layer signaling as in thecase of R-PDCCH, dynamic switching between transmission methods orallocation methods by ePDCCH is possible.

A case has been described in FIG. 18 where ePDCCH candidate numberswhich become references for switching between transmission methods andallocation methods are configured respectively. However, for example,base station 100 may configure an ePDCCH candidate number which becomesa switching reference for one of a transmission method and an allocationmethod, configure a distance (number width) from the configured ePDCCHcandidate number, and thereby identify an ePDCCH candidate number whichbecomes the other switching reference. That is, an ePDCCH candidatenumber which becomes a switching reference for one of the transmissionmethod and allocation method and the distance for identifying the otherswitching reference may be indicated from base station 100 to terminal200.

OPERATION EXAMPLE 4-2

A case will be described in operation example 4-2 where Embodiments 1 to3 and operation example 4-1 are combined. Here, although a case will bedescribed as an example where operation example 1-2 of Embodiment 1 andoperation example 4-1 are combined, without being limited to thiscombination, other operation examples may also be combined with eachother.

For example, as shown in FIG. 19, ePDCCH candidates with ePDCCHcandidate numbers #0 to #11 correspond to aggregation level 1, ePDCCHcandidates with ePDCCH candidate numbers #12 to #23 correspond toaggregation level 2, ePDCCH candidates with ePDCCH candidate numbers #24to #27 correspond to aggregation level 4 and ePDCCH candidates withePDCCH candidate numbers #28 to #31 correspond to aggregation level 8.

In FIG. 19, in base station 100, configuration section 102 configuresePDCCH candidate number #22 corresponding to aggregation level 2 as areference for switching between transmission methods of ePDCCH.Furthermore, configuration section 102 configures ePDCCH candidatenumber #19 as a reference for switching between allocation methods ofePDCCH.

Thus, as shown in FIG. 19, control signal processing section 205 ofterminal 200 identifies a transmission method, allocation method andaggregation level of each of ePDCCH candidate numbers #0 to #31 andperforms blind decoding based on the identified configuration.

By so doing, in operation example 4-2, effects similar to those ofoperation example 1-2 and operation example 4-1 can be achieved.

Embodiment 5

A method for indicating a DCI format will be described in the presentembodiment.

Note that a base station and a terminal according to the presentembodiment have basic configurations common to those of base station 100and terminal 200 according to Embodiment 1, and therefore theirconfigurations will be described with reference to FIGS. 7 and 8.

In ePDCCH, one transmission mode is configured for downlink (DL) anduplink (UL) for each terminal. Each terminal performs blind decoding(monitoring) on ePDCCH in a DCI format for UL grant and a DCI format forDL assignment.

For example, in C-SS (common search space), a terminal performs blinddecoding on two sizes (DCI sizes) of DCI format. For example, theterminal performs blind decoding 6 times (4 times and 2 times forrespective aggregation levels 4 and 8) for each DCI size.

(1) DCI format 0/1A/3/3A (these are of the same size)

(2) DCI format 1C

For example, in UE-SS (UE specific search space), the DCI format inwhich the terminal performs blind decoding differs depending on thetransmission mode.

More specifically, when the transmission mode is a UL single antennaport mode, the terminal performs blind decoding on DCI formats of twoDCI sizes. For example, the terminal performs blind decoding on each DCIsize 16 times (6 times, 6 times, 2 times and 2 times for respectiveaggregation levels 1, 2, 4 and 8).

(1) DCI format 0/1A

(2) DCI format X (downlink transmission mode dependent DCI, candidatesfor X are 1B, 1D, 1, 2, 2A, 2B and 2C)

On the other hand, when the transmission mode is a UL multi antenna portmode, the terminal performs blind decoding on DCI formats of thefollowing 3 DCI sizes. For example, the terminal performs blind decodingon each DCI size 16 times (6 times, 6 times, 2 times and 2 times forrespective aggregation levels 1, 2, 4 and 8).

(1) DCI format 0/1A

(2) DCI format X (downlink transmission mode dependent DCI)

(3) DCI format Y (uplink transmission mode dependent DCI, a candidatefor Y is 4 (in case of 3GPP rel.10))

Studies are currently being carried out on whether or not all theaforementioned DCIs are supported for ePDCCH, but one DCI is configuredfor at least each of DCI for DL assignment and DCI for UL grant in theterminal.

The present embodiment associates each of a plurality of ePDCCHcandidates making up search spaces in ePDCCH with types of size (DCIsizes) of a plurality of DCI formats. This allows terminal 200 toidentify a DCI format of what DCI size is assigned based on an ePDCCHcandidate number. That is, terminal 200 performs blind decoding on onlyDCI formats of DCI sizes identified in each ePDCCH candidate.

First, C-SS will be described.

For two types of DCI format of different DCI sizes (DCI formats0/1A/3/3A (these are of the same size) and DCI format 1C), base station100 and terminal 200 associate, for example, DCI format 0/1A/3/3A witheven-numbered ePDCCH candidate numbers and associate DCI format 1C withodd-numbered ePDCCH candidate numbers.

Thus, for example, in terminal 200, control signal processing section205 performs blind decoding assuming DCI format 0/1A/3/3A on ePDCCHcandidates whose modulo operation (ePDCCH candidate number mod 2)=0 andperforms blind decoding assuming DCI format 1C on ePDCCH candidateswhose (ePDCCH candidate number mod 2)=1.

Next, UE-SS will be described.

For two types of DCI format (DCI format 0/1A (these are of the samesize) and DCI format X (downlink transmission mode dependent DCI)) ofdifferent DCI sizes, base station 100 and terminal 200 associate, forexample, DCI format 0/1A with even-numbered ePDCCH candidate numbers andassociate DCI format X with odd-numbered ePDCCH candidate numbers.

Thus, for example, in terminal 200, control signal processing section205 performs blind decoding assuming DCI format 0/1A on ePDCCHcandidates whose modulo operation (ePDCCH candidate number mod 2)=0 andperforms blind decoding assuming DCI format X on ePDCCH candidates whose(ePDCCH candidate number mod 2)=1.

On the other hand, for three types of DCI format (DCI format 0/1A (theseare of the same size), DCI format X (downlink transmission modedependent DCI) and DCI format Y (uplink transmission mode dependentDCI)) of different DCI sizes, base station 100 and terminal 200associate, for example, DCI format 0/1A with ePDCCH candidates whosemodulo operation (ePDCCH candidate number mod 3)=0, associate DCI formatX with ePDCCH candidates whose (ePDCCH candidate number mod 3)=1 andassociate DCI format Y with ePDCCH candidates whose (ePDCCH candidatenumber mod 3)=2.

Thus, for example, in terminal 200, control signal processing section205 performs blind decoding assuming DCI format 0/1A on ePDCCHcandidates whose (ePDCCH candidate number mod 3)=0, performs blinddecoding assuming DCI format X on ePDCCH candidates whose (ePDCCHcandidate number mod 3)=1 and performs blind decoding assuming DCIformat Y on ePDCCH candidates whose (ePDCCH candidate number mod 3)=2.

By so doing, terminal 200 can identify a DCI size which is a blinddecoding target based on the ePDCCH candidate number, and signaling forDCI format indication is unnecessary. For example, compared to a case asshown in FIG. 4 where a DCI format is indicated for each ePDCCHcandidate, it is possible to reduce the number of bits necessary toindicate the DCI format from N bits (32 bits in FIG. 4) in the case oftwo types and 2 N bits (64 bits in FIG. 4) in the case of three types to0 bits.

When the present embodiment is combined with, for example, Embodiments 1to 4, it is possible to uniformly assign DCI formats of different DCIsizes to each transmission method, each aggregation level or eachallocation method. As an example, in operation example 1-2 of Embodiment1, ePDCCH candidate numbers are assigned in ascending order from ePDCCHcandidates corresponding to lower aggregation levels. Thus, for example,by associating ePDCCH candidate numbers with DCI sizes based on modulooperation corresponding to ePDCCH candidate numbers, it is possible touniformly assign different DCI sizes among a plurality of aggregationlevels.

In the present embodiment, for example, when the number of resources ofePDCCH candidates at aggregation level 1 is small, only DCI format 0/1Amay be supported at the aggregation level of UE-SS.

A case has been described in the present embodiment where ePDCCHcandidate numbers are associated with DCI sizes based on modulooperations on ePDCCH candidate numbers, but an ePDCCH candidate numberfor switching between DCI formats may be indicated from base station 100to terminal 200. For example, in FIG. 20, ePDCCH candidate number #13 isindicated as a position of switching between DCI format 0/1A and DCIformat X, and ePDCCH candidate number #26 is indicated as a position ofswitching between DCI format X and DCI format Y. As shown in FIG. 20,when a ratio of the number of ePDCCH candidates corresponding to eachaggregation level is configured, each DCI format is assigned a number ofePDCCH candidates corresponding to the ratio of the number of ePDCCHcandidates at each aggregation level respectively. For example, in FIG.20, 13 ePDCCH candidates with ePDCCH candidate numbers #0 to #12corresponding to DCI format 0/1A, 13 ePDCCH candidates with ePDCCHcandidate numbers #13 to #25 corresponding to DCI format X and 6 ePDCCHcandidates with ePDCCH candidate numbers #26 to #31 corresponding to DCIformat Y0/1A are assigned to each aggregation level respectively inaccordance with the ratio.

Embodiment 6

A case will be described in the present embodiment where transmissiondiversity using single antenna port is supported.

Note that a base station and a terminal according to the presentembodiment have basic configurations common to those of base station 100and terminal 200 according to Embodiment 1, and therefore theirconfigurations will be described with reference to FIGS. 7 and 8.

Transmission diversity using single antenna port is, for example, RBF(Random Beam Forming) and CDD. In RBF, a diversity gain of precoding canbe obtained by changing precoding for each RB in the frequency domain ortime domain. In CDD, a frequency diversity gain can be obtained bychanging a channel in the frequency domain.

Here, within the range in which channel estimation accuracy does notdeteriorate, if antenna ports to be used are not changed betweentransmission diversity using single antenna port and single antenna porttransmission (that is, transmission by precoding based on feedback), thebase station can switch between transmission methods without beingnoticed by the terminal. That is, since the terminal performs channelestimation in RB pairs or in units of a plurality of RBs, the terminalcan receive signals without being aware of transmission diversity usingsingle antenna port or single antenna port transmission that performsfeedback-based precoding as long as the amount of variation within therange in which channel estimation is performed is such an extent thatdoes not affect deterioration of channel estimation accuracy.

In transmission diversity using single antenna port, power isconcentrated on single antenna port in RS (Reference Signal), and it isthereby possible to improve channel estimation accuracy compared to SFBCusing two or more antenna ports or transmission diversity using multipleantenna ports such as long delay CDD.

However, if antenna ports assigned as terminal-specific ones for singleantenna port transmission for feedback-based precoding are used asantenna ports for transmission diversity using single antenna port asthey are, it is difficult to share RSs among terminals. This leads to aproblem that RS power is distributed to multiple antenna ports. Forexample, a case will be described where a terminal assigned antenna port7 for single antenna port transmission and a terminal assigned antennaport 8 are CDM-multiplexed (Code Division Multiplexing) using the sameRB pair. In this case, also at the time of transmission diversity usingsingle antenna port, if the above-described antenna ports are used asthey are, both CDM-multiplexed antenna ports 7 and 8 are used and RSpower is thereby distributed and RS power at each antenna portdecreases.

The aforementioned problem with power may possibly occur in acombination of CDM-multiplexed antenna ports 7 and 8 or a combination ofantenna ports 9 and 10 in particular. That is, RS power is distributedto the antenna ports in such combinations of antenna ports.

Here, in single antenna port transmission that performs feedback-basedprecoding, it is necessary to vary precoding by assigning antenna portsdiffering from one terminal to another to regions having good receivingquality. On the other hand, in transmission diversity using singleantenna port, it is preferable to concentrate RS power using the sameantenna port among terminals in a region having poor receiving quality.

Moreover, since QPSK modulation is assumed to be applied in ePDCCH, evenwhen RS power differs from ePDCCH power, the terminal can receiveePDCCH.

As described above, when a low aggregation level (e.g., level 1 or 2) isused, single antenna port transmission that selects precoding based onfeedback information is effective. On the other hand, when a highaggregation level (e.g., level 4 or 8) is used, transmission diversityis effective to obtain a diversity gain.

Thus, in the present embodiment, base station 100 switches betweenantenna ports to be used in accordance with the aggregation level.

Furthermore, as shown in FIG. 21, base station 100 indicates antennaports to be used in 2 bits (00, 01, 10, 11) to each terminal 200.

As shown in FIG. 21, while one of antenna ports 7, 8, 9 and 10 is usedat aggregation levels 1 and 2, one of antenna ports 7 and 9 is used ataggregation levels 4 and 8. More specifically, as shown in FIG. 21,different antenna ports 7 and 8 are configured with ‘00’ and ‘01’ ataggregation levels 1 and 2, whereas at aggregation levels 4 and 8, thesame antenna port 7 is configured. Similarly, as shown in FIG. 21,different antenna ports 9 and 10 are configured with ‘10’ and ‘11’ ataggregation levels 1 and 2, whereas at aggregation levels 4 and 8, thesame antenna port 9 is configured.

By so doing, different antenna ports are assigned to different terminals200 at low aggregation levels (levels 1 and 2 in FIG. 21). Therefore, inthe case of single antenna port transmission that performsfeedback-based precoding, different precoding can be configured forterminals 200.

On the other hand, at high aggregation levels (levels 4 and 8 in FIG.21), the same antenna port is assigned to different terminals 200. Thus,when terminals 200 using transmission diversity using single antennaport are multiplexed in the same RB pair, it is possible to share thesame antenna port and concentrate and increase power per RS antennaport, and thereby improve channel estimation accuracy.

When antenna ports to be used do not change depending on the aggregationlevel (e.g., ‘00’ or ‘10’ shown in FIG. 21), terminal 200 can receivesignals without being aware of single antenna port transmission thatperforms feedback-based precoding or transmission diversity using singleantenna port. Thus, in this case, base station 100 may use anytransmission method for terminal 200 for which the antenna port isconfigured.

It can be said that switching between antenna ports in the presentembodiment is applied by replacing switching between single antenna porttransmission and diversity using multiple antenna ports according toEmbodiments 1 to 5 with switching between antenna ports 7, 8, 9 and 10to be used for single antenna port transmission and antenna ports 7 and9 to be used for single antenna port transmission with limited antennaports.

In the present embodiment, a change in the number of antenna ports maybe indicated from base station 100 to terminal 200 so as to switch amongthree transmission methods: single antenna port transmission,transmission diversity using multiple antenna ports, and transmissiondiversity using single antenna port.

For example, when channel quality is extremely poor, transmissiondiversity using single antenna port with high RS channel estimationaccuracy is appropriate. On the other hand, when channel estimationaccuracy can be secured but channel quality is poor to a certain degree,transmission diversity using multiple antenna ports is appropriate. Whenchannel quality is good and the moving speed of terminal 200 isrelatively slow, obtaining a frequency scheduling gain by single antennaport transmission that performs feedback-based precoding is appropriate.Base station 100 may indicate an ePDCCH candidate number correspondingto a position of switching between these transmission methods.

In an example shown in FIG. 22, base station 100 indicates ePDCCHcandidate numbers #17 and #26 to terminal 200. Thus, as shown in FIG.22, terminal 200 performs blind decoding assuming single antenna porttransmission with ePDCCH candidate numbers #0 to #16, assumingtransmission diversity using multiple antenna ports with ePDCCHcandidate numbers #17 to #25 and assuming transmission diversity usingsingle antenna port with ePDCCH candidate numbers #26 to #31.

When the total number of ePDCCH candidates is assumed to be N, thenumber of bits necessary to indicate an ePDCCH candidate which becomesthe above-described reference for switching between transmission methodsis 2*ceil (log₂(N+1)) bits. For example, since N=32 in FIG. 22, 2*ceil(log₂(N+1))=12bits. When two indications from base station 100 toterminal 200 are both #N (#32 in FIG. 22), the transmission method forall ePDCCH candidates may be assumed to be single antenna porttransmission and when the two indications are both #0, the transmissionmethod for all ePDCCH candidates may be assumed to be transmissiondiversity using single antenna port.

In FIG. 22, as in the case of Embodiment 1, in order to allow theantenna port for single antenna port transmission to uniquely identifyantenna ports for transmission diversity using multiple antenna ports,antenna ports to be used for both transmission methods may be associatedwith each other beforehand (e.g., see FIG. 13). Alternatively, only thesame antenna ports may be configured beforehand to be always used asantenna ports for transmission diversity using multiple antenna ports.

Although a case has been described in the present embodiment where 32ePDCCH candidates are used as shown, for example, in FIG. 22, the numberof ePDCCH candidates is not limited to 32. As in the case of Embodiment1, ePDCCH candidates for which transmission methods are switched may bea region, to the whole of which control information relating to downlink(DL) is mapped or may be a region, to the whole of which controlinformation relating to uplink (UL) is mapped or may be a region inwhich a region to which control information relating to downlink (DL) ismapped and a region to which control information relating to uplink (UL)is mapped are mixed. For example, the numbers of ePDCCH candidatescorresponding to downlink control information for aggregation levels 1,2, 4 and 8 may be assumed to be 6, 6, 2 and 2 respectively and thenumbers of ePDCCH candidates corresponding to control information ofuplink control information may be assumed to be 6, 6, 2 and 2respectively. As in the case of FIG. 22, the total number of ePDCCHcandidates in this case is also 32.

The ePDCCH candidates for which transmission methods are switched may bea region that makes up a search space (UE-SS) specific to terminal 200or may be a region that makes up a search space (C-SS) common to aplurality of terminals 200 or may be a region in which the regionsmaking up UE-SS and C-SS respectively are mixed.

Each embodiment of the present invention has been described thus far.

Other Embodiments

[1]

In each of the embodiments described above, the term “antenna port”refers to a logical antenna including one or more physical antennas. Inother words, the term “antenna port” does not necessarily refer to asingle physical antenna, and sometimes refers to an array antennaincluding a plurality of antennas, for example.

For example, in 3GPP LTE, how many physical antennas are included in theantenna port is not defined, but the antenna port is defined as theminimum unit allowing the base station to transmit a different referencesignal.

In addition, an antenna port may be specified as a minimum unit to bemultiplied by a precoding vector weighting.

[2]

In each embodiment described above, the present invention is configuredwith hardware by way of example, but the invention may also be providedby software in concert with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology, for example.

A reception apparatus according to the present disclosure includes: areception section that receives a signal mapped to one of a plurality ofmapping candidates; and a processing section that performs blinddecoding on the plurality of mapping candidates using one of a firsttransmission method using a single antenna port to perform precodingbased on feedback information from a reception apparatus in accordancewith an aggregation level configured for each of the plurality ofmapping candidates, and a second transmission method to performtransmission diversity using multiple antenna ports.

In the reception apparatus according to this disclosure, the processingsection performs blind decoding on a mapping candidate corresponding toan aggregation level lower than a predetermined value among theplurality of mapping candidates using the first transmission method andperforms blind decoding on a mapping candidate corresponding to anaggregation level equal to or higher than the predetermined value usingthe second transmission method.

In the reception apparatus according to this disclosure, the mappingcandidates are assigned numbers in ascending order from a mappingcandidate corresponding to a lower aggregation level, the receptionsection receives a first number assigned to a mapping candidatecorresponding to a position of switching between transmission methodsamong the numbers assigned to the plurality of mapping candidates, andthe processing section performs blind decoding on a mapping candidateassigned a number lower than the first number using the firsttransmission method and performs blind decoding on a mapping candidateassigned a number equal to or greater than the first number using thesecond transmission method.

In the reception apparatus according to this disclosure, the mappingcandidates are assigned numbers in ascending order from a mappingcandidates corresponding to an aggregation level lower than L (L is anatural number) to a mapping candidate corresponding to an aggregationlevel equal to or higher than L; the reception section receives a firstnumber assigned to a mapping candidate corresponding to a position ofswitching between transmission methods among the numbers assigned to theplurality of mapping candidates; and the processing section performsblind decoding on a mapping candidate assigned a number lower than thefirst number using the first transmission method and performs blinddecoding on a mapping candidate assigned a number equal to or greaterthan the first number using the second transmission method.

In the reception apparatus according to this disclosure, when theplurality of aggregation levels are included in the aggregation levelequal to or higher than L, the reception section performs blind decodingusing one of the first transmission method and the second transmissionmethod at the plurality of aggregation levels.

In the reception apparatus according to this disclosure, a second numberindicating a number assigned to a mapping candidate corresponding to aposition of switching between different aggregation levels is configuredto be variable among the plurality of mapping candidates.

In the reception apparatus according to this disclosure, the secondnumber is configured so that a ratio of a number of mapping candidatescorresponding to more frequently used aggregation levels to a totalnumber of the plurality of mapping candidates is higher.

In the reception apparatus according to this disclosure, the receptionsection receives the second number; and the processing sectionconfigures an aggregation level for each of the plurality of mappingcandidates based on the second number.

In the reception apparatus according to this disclosure, the pluralityof mapping candidates comprise a first mapping candidate group to whicha signal specific to each reception apparatus is mapped and a secondmapping candidate group to which a signal common to a plurality ofreception apparatuses or a signal specific to each reception apparatusis mapped; in the first mapping candidate group, a mapping candidate isassigned a number in ascending order from a mapping candidatecorresponding to a lower aggregation level; and in the second mappingcandidate group, a mapping candidate is assigned a number greater than amaximum number assigned to a mapping candidate included in the firstmapping candidate group in ascending order from a mapping candidatecorresponding to a lower aggregation level.

In the reception apparatus according to this disclosure, the pluralityof mapping candidates comprise a first mapping candidate group to whicha signal specific to each reception apparatus is mapped and a secondmapping candidate group to which a signal common to a plurality ofreception apparatuses or a signal specific to each reception apparatusis mapped; in the first mapping candidate group, a mapping candidate isassigned a number in ascending order from a mapping candidatecorresponding to an aggregation level lower than L; and in the secondmapping candidate group, a mapping candidate is assigned a numbergreater than a maximum number assigned to a mapping candidate includedin the first mapping candidate group in ascending order from a mappingcandidate corresponding to an aggregation level equal to or greater thanL.

In the reception apparatus according to this disclosure, the signal istransmitted using one of a plurality of formats; the plurality ofmapping candidates are associated with the plurality of formatsrespectively; and the processing section performs blind decoding on onlythe formats associated with the plurality of mapping candidates.

A transmission apparatus according to the present disclosure includes: aprecoding section that performs precoding on a signal mapped to one of aplurality of mapping candidates using one of a first transmission methodusing a single antenna port to perform precoding based on feedbackinformation from a reception apparatus in accordance with an aggregationlevel configured for each of the plurality of mapping candidates, and asecond transmission method that performs transmission diversity usingmultiple antenna ports; and a transmission section that transmits theprecoded signal.

A reception method according to the present disclosure includes:receiving a signal mapped to one of a plurality of mapping candidates;and performing blind decoding on the plurality of mapping candidatesusing one of a first transmission method using a single antenna port toperform precoding based on feedback information from a receptionapparatus in accordance with an aggregation level configured for each ofthe plurality of mapping candidates, and a second transmission method toperform transmission diversity using multiple antenna ports.

A transmission method according to the present disclosure includes:performing precoding on a signal mapped to one of a plurality of mappingcandidates using one of a first transmission method using a singleantenna port to perform precoding based on feedback information from areception apparatus in accordance with an aggregation level configuredfor each of the plurality of mapping candidates, and a secondtransmission method that performs transmission diversity using multipleantenna ports; and transmitting the precoded signal.

The disclosures of the specifications, the drawings, and the abstractsincluded in Japanese Patent Applications No. 2012-031653 filed on Feb.16, 2012, and No. 2012-055433 filed on Mar. 13, 2012 are incorporatedherein by reference in their entireties.

INDUSTRIAL APPLICABILITY

The present invention is useful in mobile communication systems.

REFERENCE SIGNS LIST

100 Base station

200 Terminal

101 Assignment information generation section

102 Configuration section

103, 206 Error correction coding section

104, 207 Modulation section

105 Precoding section

106, 208 Signal assignment section

107, 209 Transmission section

108, 201 Reception section

109, 203 Demodulation section

110, 204 Error correction decoding section

202 Signal separating section

205 Control signal processing section

1. A communication apparatus comprising: a precoder which, in operation,applies a first precoding corresponding to single-antenna transmissionto a downlink control signal when a localized allocation is used and, inoperation, applies a second precoding corresponding to multi-antennatransmission to the downlink control signal when a distributedallocation is used, for each of a plurality of Enhanced PhysicalDownlink Control Channel (EPDCCH) candidates configured in a dataregion, wherein a plurality of first aggregation levels for thedistributed allocation at least partially overlaps with a plurality ofsecond aggregation levels for the localized allocation and includes atleast one more aggregation level that is greater than any one of thesecond aggregation levels, and wherein each of the EPDCCH candidates atan aggregation level comprises a number of resources that corresponds tothe aggregation level; and a transmitter which, in operation, transmitsthe precoded downlink control signal using a single antenna port whenthe localized allocation is used and, in operation, transmits theprecoded downlink control signal using two antenna ports when thedistributed allocation is used.
 2. The communication apparatus accordingto claim 1, wherein the precoder, in operation, applies the secondprecoding corresponding to multi-antenna transmission to an EPDCCHcandidate whose aggregation level is equal to or greater than athreshold value.
 3. The communication apparatus according to claim 1,wherein the second precoding corresponding to multi-antenna transmissionis a precoding for transmission diversity.
 4. The communicationapparatus according to claim 1, wherein the transmitter comprises threeor more antenna ports; the single antenna port is selected from amongthe three or more antenna ports when the localized allocation is used;and the two antenna ports used for the distributed allocation are asubset of the three or more antenna ports.
 5. The communicationapparatus according to claim 4, wherein the three or more antenna portsprovide several subsets and one of the several subsets is selected whenthe distributed allocation is used.
 6. The communication apparatusaccording to claim 1, wherein resources for the localized allocation arelocalized and resources for the distributed allocation are distributedin a frequency domain.
 7. A communication method comprising: applying afirst precoding corresponding to single-antenna transmission to adownlink control signal when a localized allocation is used and applyinga second precoding corresponding to multi-antenna transmission to thedownlink control signal when a distributed allocation is used, for eachof a plurality of Enhanced Physical Downlink Control Channel (EPDCCH)candidates configured in a data region, wherein a plurality of firstaggregation levels for the distributed allocation at least partiallyoverlaps with a plurality of second aggregation levels for the localizedallocation and includes at least one more aggregation level that isgreater than any one of the second aggregation levels, and wherein eachof the EPDCCH candidates at an aggregation level comprises a number ofresources that corresponds to the aggregation level; and transmittingthe precoded downlink control signal using a single antenna port whenthe localized allocation is used and transmitting the precoded downlinkcontrol signal using two antenna ports when the distributed allocationis used.
 8. The communication method according to claim 7, wherein thesecond precoding corresponding to multi-antenna transmission is appliedto an EPDCCH candidate whose aggregation level is equal to or greaterthan a threshold value.
 9. The communication method according to claim7, wherein the second precoding corresponding to multi-antennatransmission is a precoding for transmission diversity.
 10. Thecommunication method according to claim 7, wherein the single antennaport is selected from among three or more antenna ports when thelocalized allocation is used; and the two antenna ports used for thedistributed allocation are a subset of the three or more antenna ports.11. The communication method according to claim 10, wherein the three ormore antenna ports provide several subsets and one of the severalsubsets is selected when the distributed allocation is used.
 12. Thecommunication method according to claim 7, wherein resources for thelocalized allocation are localized and resources for the distributedallocation are distributed in a frequency domain.